Can I suggest you trial KavoomKM...

http://www.kavoom.biz/km/km_overview.html

I use it, along with 2xKeyclone, to 5 box in a 1+4 formation and wouldn't be without it now!

I use the keyboard and mouse from PC1 and when I move off the right hand edge of Monitor1 the keyboard and mouse instantly "move" over to PC2/Monitor2.
The keyboard and mouse for PC2 are hidden away.
You really wouldn't know that you're not on 1 PC with 2 monitors.

You do have to buy a licence but you can install it and trial it (IIRC you get to trial it for 30m or so before it stops working... I knew I was buying it well before then).